The present invention applies generally to the use of optical reflection pickup units to detect randomly placed small or microscopic particles on a relatively smooth and reflective surface. One embodiment of the invention is the use of an optical pickup unit to detect toner particles on an electrophotographic imaging surface that have escaped removal during the surface cleaning process.
Many manufacturing and imaging processes require periodic removal of dust and other microscopic particles from relatively smooth surfaces. Examples include, without limitation, cleaning of vessels, tubes, molds, forms, and other holding, processing, shaping, and transferring equipment used in clean-room environments and in other environments where removal of stray particles is important for imaging, purification, or contamination purposes. Often, a primary cleaning process is used, and, depending upon its efficacy, sufficient cleaning may be assumed. Where the primary cleaning process is not dependable for such assurance, where the cleaning system is understood to degrade over time, or where no cleaning system is used, it would be useful to employ an accurate and repeatable system for detecting and measuring stray particles that remain on relatively smooth surfaces of the equipment that is desired to be clean before or during the next use.
One such situation described in the preceding paragraph occurs in electrostatographic imaging systems such as electrophotographic printers. Modern toners range in size from about 4 microns to about 20 microns. After toner is imaged on a drum, belt, or other charged imaging surface, such toner is transferred to a copy sheet. Transfer of such toner is known not to be complete. A primary cleaning system is accordingly employed post-imaging in order to prepare the imaging surface for recharging and reuse. Primary cleaning systems known in the art generally comprise either brushes or blades or combinations of both. Such cleaning systems are known to degrade over time, requiring periodic replacement. Even without cleaning degradation, some stray particles often escape the cleaning system.
When designing the projected maintenance schedule of a new printer, thousands of images are typically run in order to develop a statistical understanding of the rate at which primary cleaning systems degrade and to predict the time at which preventive maintenance should occur. Current methods for detecting degradation of the cleaning system generally comprise either close human inspection of copy sheets or the imaging surface to detect unacceptable levels of stray toner and debris that escaped cleaning or inspection of the amount of post-cleaning stray toner and debris that is removed from the imaging surface by tape, cleaning fluids, vacuums, or properly charged rollers. Both methods of inspection (inspection of stray toner and debris on surfaces or inspection of stray toner and debris after removal) are inaccurate and non-reproducible due to the inability of humans to quantitatively measure small and randomly placed quantities. Nevertheless, with much testing and inspection, a degradation profile is statistically generated for the applicable cleaning system. Because of wide statistical deviations in determinations of unacceptable cleaning results, the final maintenance schedule tends to call for replacement or repair of cleaning elements somewhat earlier than would be the case with better measurements resulting in smaller statistical deviations in the cleaning measurement results.
Once a printer is launched and in normal use, maintenance personnel and operators monitor cleaning efficacy using the same techniques described above. Because measurement of toner and debris left on copy or imaging surfaces or removed by tape or other removal techniques is inherently inaccurate and non-reproducible, those monitoring cleaning efficacy often actually replace cleaning elements too often or too infrequently, resulting either in higher maintenance costs or unnecessarily poor image quality.
It would be desirable to invent an accurate and reproducible stray particle detection system that produces measurable and predictive results. It is also desirable that such a system be able to detect even single particles ranging from about 1 micron to a few tens of microns in size, even if not visually detectable with human eyes.
One embodiment of the invention is a method for detecting one or more particles on a surface, such surface having areas clear of particles and such particles having a profile, such method comprising: focusing collimated light upon a clear area of the surface; measuring, with a sensor, the strength of signal reflected from the clear area of the surface; traversing the focused collimated light over the surface until it illuminates a particle; measuring, with a sensor, the strength of signal reflected from the particle; comparing with the strength of signal reflected from a clear area with the strength of signal reflected from the particle; and determining the existence of the particle by the comparison of the signals from the clear area and the particle.
Another embodiment of the invention is a method for detecting one or more depression defects on a surface, such surface having areas clear of particles and such depression defects having a profile, such method comprising: focusing collimated light upon a clear area of the surface; measuring, with a sensor, the strength of signal reflected from the clear area of the surface; traversing the focused collimated light over the surface until it illuminates a depression defect; measuring, with a sensor, the strength of signal reflected from the depression defect; comparing with the strength of signal reflected from a clear area with the strength of signal reflected from the depression defect; and determining the existence of the depression defect by the comparison of the signals from the clear area and the depression defect.
Yet another embodiment of the invention is a device for detecting particles on a surface, such surface having areas clear of particles, and such device comprising: a plurality of collimated light sources wherein the light from each is focused on a spot on the surface; a plurality of sensors, each coupled with a light source, for detecting light reflected from the surface from the coupled light source; wherein more light from a light source is reflected to the coupled sensor from clear areas of the surface than from particles.